A method of using an error rate of errors accumulated on a head-by-head basis has hitherto been known as a method of detecting a sign of failure of a hard disk apparatus. However, the conventional method was incapable of distinguishing between an error due to a failure of a head and an error due to abnormality (e.g., flaw produced on a storage surface, an impurity adhered onto the storage surface, and other equivalent causes) of a platter 101.
When the head gets into a failure, the whole storage surface undergoing read and write by the head is disabled from being used. By contrast, when the abnormality occurs in the platter, areas other than the area having the occurrence of the abnormality are still usable. Thus, requested maintenance (for preserving data) differed depending on causes of the errors, and hence the conventional method incapable of distinguishing between the causes of the errors was hard to perform the proper maintenance even when detecting the sign of failure.